The present invention relates to a support structure and a method for supporting an electromagnetic coupling between propeller shafts of a four-wheeled drive vehicle.
Japanese Patent Provisional Publication No. 10-213164 discloses a coupling (i.e. a drive power delivery unit) 501, which is exemplarily shown in FIG. 1.
The coupling 501 is located in a drive power delivery system for rear wheels of the four-wheeled drive vehicle for controlling coupling or uncoupling states of the rear wheels with respect to an engine and controlling the magnitude of drive power to be delivered to the rear wheels.
The coupling 501 is comprised of a rotational case 503, an inner shaft 505, a main clutch 507 of the multi-plate type, a pressure plate 509, an armature 511, an intermediate cam member 513, a first cam 515, a second cam 517, a spring 519, and an electromagnet 521 and a controller (not shown).
The rotational case 503 and the inner shaft 505 are located in a concentric fashion for rotational movement relative to one another, with the inner shaft 505 being disposed inside the rotational case 503.
The rotational case 503 is coupled to a propeller shaft 523 remaining closer to a transfer unit (not shown). Also, the inner shaft 505 is coupled to a propeller shaft 525, remaining closer to a rear differential unit, through a spline connection and is coupled through the propeller shaft 525 to the rear differential unit (which serves to distribute the drive power of the engine to left and right rear wheels).
The pressure plate 509 and the armature 511 are coupled to an inner circumferential periphery of the rotational case 503 through spline connections, respectively.
Further, the intermediate cam member 513 is located between the pressure plate 509 and the armature 511 for rotational movement relative to one another.
The first cam 515 is interposed between the armature 511 and the intermediate cam member 513 and is constructed of cam recesses 527 formed at an outer circumferential periphery of the intermediate cam member 513, and rollers 529 engaging the respective cam recesses 527.
The cam recesses 527 are equidistantly formed on the outer periphery of the intermediate cam member 513 in a circumferential direction, with each recess being shaped in a slanted profile with respect to an axial direction. Also, the rollers 529 are supported with the armature 511 for rotational movement.
The second cam 517 is of a ball cam, which is interposed between the pressure plate 509 and the intermediate cam member 513.
The spring 519 is disposed between the armature 511 and the intermediate cam member 513 to urge the intermediate cam member 513 toward the cam 517 to absorb looseness for thereby improving a response of the cam 517.
Further, in an event that an excitation of the electromagnet 521 is interrupted, the spring 519 serves to restore the armature 511 to its neutral position in a rotational direction to allow the intermediate cam member 513 to be restored to a neutral position in an axial direction, thereby precluding an needless torque from being produced.
Connected to the rotational case 503 is a rotor 531 which forms a magnetic flux path and which is formed with an axially extending annular cavity 535 in which a core 533 of the electromagnet 521 is received with a suitable amount of air gap.
Further, interposed between an outer circumferential periphery of the core 533 and the rotor 531 is a seal 537, with another seal 539 being disposed between an inner circumferential periphery of the core 533 and the inner shaft 505. The seals 537, 539 serve to preclude oil from leaking from the rotational case 503 while preventing entry of water or dusts from outside.
The rotor 531 is formed with axially facing contact surfaces 541 to be brought into contact with the armature 511, with an air gap 543 being formed between the armature 511 and the contact surfaces 541.
The controller serves to control the excitation of the electromagnet 521, an exciting current and an interruption of the excitation of the electromagnet 521.
Upon excitation of the electromagnet 521, a magnetic flux flow loop 545 is created in a magnetic flux path involving the air gap 543, thereby attracting the armature 511.
Upon attraction of the armature 511, the rollers 529 are moved to urge the cam recesses 527 of the intermediate cam member 513 to actuate the first cam 515 by which the intermediate cam member 513 is rotated.
Upon rotation of the intermediate cam member 513, the second cam 517 is actuated to produce a cam thrust force by which the main clutch 507 is urged via the pressure plate 515 and is brought into a coupled condition.
In such a manner, when the electromagnet 521 attracts the armature 511, its pilot function allows the first cam 515 to be operated to actuate the second cam 517 such that the coupling 501 is coupled.
When the coupling 501 is coupled, the drive power of the engine is delivered to the rear wheels to allow the vehicle to be brought into the four-wheeled drive condition, thereby improving a covering property of a rough road and a running stability in a vehicle body.
Further, when the exciting current of the electromagnet 521 is controlled, the cam force of the first cam 515 varies to vary the urging force exerted by the second cam 517, permitting the main clutch 507 to slip for thereby adjusting the drive force to be delivered to the rear wheels. Thus, controlling a drive power distribution ratio between the front and rear wheels allows driveability and operating stability of the vehicle to be improved during a circular traveling of the same.
Upon termination of excitation of the electromagnet 521, the urging force of the spring 519 allows the armature 511 (i.e. the rollers 529) to be restored to the original position such that the cam force of the first cam 515 is lost. When this occurs, the cam thrust force of the second cam 517 also disappears to release the main clutch 507 for thereby uncoupling the coupling 501 such that the vehicle is brought into a two-wheeled drive condition.
The coupling 501 is interposed between the propeller shaft 523, 525 in states exposed to the atmosphere.
In an event where the coupling 501 is located between the propeller shafts 523, 525, there are some instances where, owing to upward or downward movements of the wheels during traveling of the vehicle or the rear wheels riding on stepped portions or convex positions of the rough road during an off-road running condition, the thrust forces are directly imparted to the coupling 501 through the propeller shafts 523, 525, adversely affecting a gap between the outer plates and the inner plates of the main clutch 507 to variably change the air gap 543 between the rotor 531 and the armature 511 with a resultant degraded operating performance and degraded durability caused in the coupling 501.
Also, the presence of the coupling 501 exposed to the outside increases possibilities for the coupling 501 to conflict with obstacles such as flying stones during traveling or to conflict with the stepped portions or the convex portions of the rough road.
As a consequence, the rotational case 503 must have a strength to resist such collisions, with a resultant increase in thickness to have an increased diameter as well as increase in weight.
Also, since the rotational case 503 must have an adequate strength, a difficulty is encountered in the rotational case 503 to be formed with aluminum alloy to reduce the weight.
It is therefore an object of the present invention to provide a support structure for an electromagnetic coupling which is located on propeller shafts and which is enabled to protect the electromagnetic coupling from conflicting with obstacles, from entry of the obstacles and from being subjected to a thrust force exerted from the propeller shafts.
It is another object of the present invention to provide a method for supporting an electromagnetic coupling onto a vehicle body so as to protect the electromagnetic coupling from conflicting with obstacles, from entry of the obstacles and from being subjected to a thrust force exerted from propeller shafts of a vehicle.
According to a first aspect of the present invention, there is provided a support structure for an electromagnetic coupling located between a first propeller shaft connected to a prime mover and a second propeller shaft connected to wheels of a vehicle, said support structure comprising: a first bearing supporting said first propeller shaft and adapted to be fixedly mounted to a vehicle body; and a second bearing supporting said second propeller shaft and adapted to be fixedly mounted to said vehicle body; wherein said electromagnetic coupling is interposed between said first and second bearings.
In a case where the propeller shaft is divided into two pieces, one for the prime mover and the other for the wheels, since either one of the propeller shafts is located at a slope wherein an end of the propeller shaft closer to the bearing (which remains at a position remotest from the prime mover or the wheels) remains at a higher level than the other end, with a space between the respective propeller shafts having a maximum value in a minimum under-clearance (i.e. a road clearance).
In accordance with the present invention, the electromagnetic coupling is interposed in the above space between the bearings (i.e. the center support bearings) each having the maximum road clearance, with a resultant decrease in the possibilities in conflicting with stepped portions or convex portions of a rough road during an off-road traveling to maintain its normal operating performance.
Further, since the space between the bearings which support the relevant propeller shafts is located in the close proximity to a central area of the vehicle body which minimizes a degree of an adverse affect caused by vibrations of the vehicle body and the propeller shafts.
In addition, although the propeller shaft closer to the wheels encounters rocking movement depending on upward or downward movements of the wheels, the rocking movement is absorbed with a coupling joint mounted at an end of the propeller shaft and is interrupted from being transmitted to the electromagnetic coupling.
With such a structure, the electromagnetic coupling is less suffered from the collision with the obstacles and is protected from being adversely affected with the vibrations of the vehicle body and the propeller shafts as well as the rocking movements of the propeller shafts. This results in a minimum displacement in a distance between the outer plates and the inner plates of the clutch and an air gap between the core and the rotor, which forms a part of a magnetic flux path of the core, providing a stable operating stability and an increased durability.
Also, since the electromagnetic coupling has a reduced degree of vibration and is close to the vehicle body, it is easy for the lead wires of the electromagnet to be pulled out, and a disconnection of the lead wires is minimized.
According to a second aspect of the present invention, there is provided a method of supporting an electromagnetic coupling on a vehicle body of a vehicle, said method comprising: locating said electromagnetic coupling between a first propeller shaft connected to a prime mover and a second propeller shaft connected to wheels of a vehicle; supporting said first propeller shaft with a first bearing; supporting said second propeller shaft with a second bearing; supporting said electromagnetic coupling between said first and second bearings; and fixedly mounting said first and second bearings onto said vehicle body.
Other aspect and advantages of the invention will become more apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.